1. Field of the Invention
The present invention relates to a transmitting and receiving apparatus of a time division full-duplex spread spectrum communication system and, more particularly, to a transmitting and receiving apparatus of a time division full-duplex communication system for transmitting or receiving one oscillation frequency during transmission or reception in synchronization with a lock time by using a phase locked loop (PLL) which rapidly converts its frequency according to a control voltage.
A transmitting and receiving apparatus according to the present invention is based on Korean Application No. 59434/1995 which is incorporated herein by reference.
2. Description of the Related Art
FIG. 1 shows a conventional transmitting and receiving apparatus of a time division full-duplex spread spectrum communication system of the prior art. In FIG. 1, an antenna 20 transmits or receives data via an air line. A time division duplexer (hereinafter, referred to as TDD) 21 switches transmitting and receiving modes at regular time intervals. A low noise amplifier (hereinafter, referred to as LNA) 22 amplifies a receiving signal to an amplified level and outputs the amplified receiving signal to a first band pass filter (hereinafter, referred to as BPF) 23 when the time division duplexer 21 is switched into the receiving mode. The first band pass filter 23 receives the amplified receiving signal and passes only a signal of a given band. A low pass filter (hereinafter, referred to as LPF) 28 low pass filters a received pseudonoise (PN) code and data as a square wave signal, and converts the square wave signal into a sine wave signal. A main PLL 29 generates a main oscillation frequency in response to the PN code and data converted into the sine wave signal. A first mixer 24 lowers the receiving signal passed from the first BPF 23 by the main oscillation frequency generated from the main PLL 29, and generates a first intermediate frequency signal which is output to a second BPF 25. The second BPF 25 passes only the first intermediate frequency signal.
A first oscillator 26 generates a first oscillation frequency. A demodulator 27 mixes the first intermediate frequency signal passed from the second band pass filter 25 with the first oscillation frequency generated from the first oscillator 26 and converts the mixed signal into a second intermediate frequency signal. Further, the demodulator 27 amplifies the converted second intermediate frequency signal and demodulates the PN code and data. A second oscillator 30 generates a second oscillation frequency. A second mixer 31 mixes the second oscillation frequency signal generated from the second oscillator 30 with the main oscillation frequency generated from the main PLL 29 and generates a transmitting signal. A third BPF 32 receives the transmitting signal generated from the second mixer 31 and passes only the transmitting signal in a desired band. An amplifier 33 amplifies the transmitting signal passed from the third BPF 32 to a desired power level to be output. At this time, the time division duplexer 21 selects the transmitting mode and transmits the transmitting signal amplified from the amplifier 33 through the antenna 20 to the air line.
In the prior art transmitting and receiving apparatus of the time division full-duplex spread spectrum communication system as shown in FIG. 1, it is difficult to switch on or off the respective oscillation frequencies generated due to the use of rapid time division. The first and second oscillators implement transmitting or receiving operation at different frequencies under the state that they are continuously switched on, and thus the first and second oscillation frequencies are mutually subject to interference. Therefore, the transmitting or receiving sensitivity may deteriorate. Moreover, since two oscillators are used, the construction of a circuit is complicated and requires extra components.